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How do tires affect gas mileage?

Posted: Wednesday, February 27th 2013

Tire fuel efficiency ratingDid you know your tires can affect your gas mileage? Your tires affect everything from handling, braking and acceleration, to yes – even gas mileage.  In fact, many tire manufacturers are now featuring a fuel efficiency rating for their tire models.

But what does this really mean?

Tires affect vehicle fuel efficiency primarily through rolling resistance. Rolling resistance is defined as the measure of “force at the axle in the direction of travel required to make a loaded tire roll,” according to a report by the National Research Council (NRC). “As a tire rolls under the vehicle’s weight, its shape changes repeatedly as it experiences recurring cycles of deformation and recovery. In the process, mechanical energy otherwise available to turn the wheels is converted into heat and dissipated from the tire. More fuel must be expended to replace this lost energy. Combinations of differences in tire dimensions, design, materials, and construction features will cause tires to differ in rolling resistance as well as in many other attributes such as traction, handling, noise, wear resistance, and appearance. Once they are placed in service, tires must be properly maintained to perform as intended with respect to all attributes. The maintenance of proper inflation pressure is especially important.”

That’s a technical way of saying that rolling-resistance measures how much effort the vehicle has to put into making the tires roll along the pavement. Tires with low rolling resistance use tread design and new materials to minimize the amount of energy, in the form of gasoline, required to move the car.

For example, new materials such as Tg-F polymers used in Continental’s ProContact EcoPlus+ tires provide lower rolling resistance and therefore improved fuel efficiency and lower CO2 emissions. Goodyear’s Assurance Fuel Max Tires claim to “save up to 2,600 mi./4,000km worth of gas over the life of four tires” by using a fuel-saving tread compound which provides low rolling resistance.  Michelin’s Energy Saver A/S tires come as original equipment on several passenger cars.  These tires are touted as lasting “up to 16,000 miles longer” than the leading competitor and saving “up to $400 in gas over the life of your tires” (based on $3.75 per gallon).  These are all features which consumers have demanded – longer life, better fuel efficiency, and improved performance.

A recent study of fuel efficient tires conducted by the National Research Council “showed that current generation low rolling resistance tires offers a similar level of snow traction performance as conventional tires, while reducing fuel consumption and emissions.”

An article published on Tire Review discusses the cost saving benefits of fuel efficient tires. “Studies show that 20% to 30% of a vehicle’s fuel consumption and 24% of road vehicle CO2 emissions are tire-related. Green tires can reduce fuel consumption by 5% to 7% and have a shorter cost amortization period in comparison to other fuel-saving technologies in cars.”

But how do fuel efficient tires perform compared to “standard” tires? According to a Consumer Report’s test of the Michelin Energy Saver A/S and Cooper GFE – both tires “performed well”. The Michelin “garnered an excellent overall score, second only to its sibling the long- wearing Michelin HydroEdge. The Energy Saver has exceptionally low rolling resistance and rated Good or better in nearly every test category — same as the HydroEdge. But where the HydroEdge excels in tread life, the Energy Saver A/S was just average achieving a Good rating.” The tests showed the Cooper GFE is a “very good choice overall, suitable for all-weather conditions and low-rolling resistance, but not as low as the Michelin Energy Saver A/S.”

Tire contact patchIt’s also important to keep in mind that your tires are the only material connecting your vehicle to the road. And only a small patch of each tire, called the “contact patch”, is connected to the road at any time. If your tires are worn out – it not only impairs handling, but worn tires are likely to slip more on the road which requires the engine to work harder to move the vehicle forward. Similarly, tires with low air pressure will cause the rubber to bulge where it meets the pavement and create more driving friction (more tire surface coming in contact with the road).  Since the weight of the vehicle is not properly supported, this also will put additional strain on the engine.

A harder working engine translates to an inefficient vehicle.  Your tires can directly impact the overall performance and life of the automobile.  An overworked engine also means it uses more gas per mile than a vehicle driving on properly maintained tires.

Proper tire maintenance – including routine air pressure checks, rotations, alignments, are the best practices for extending the life of your tires and increasing your fuel efficiency.

If you have any questions about fuel efficiency ratings, rolling resistance, or driving safety, please feel free to call or stop by one of the convenient Dunn Tire locations. As always, your comments, questions and feedback are encouraged!